This invention relates to a tube and method for controlling and removing molten spatter generated during a cutting process without introducing unwanted contaminants on the cut product.
During aircraft manufacture, a Laser Trim Cell (LTC) system trims duct assembly details to a net length in preparation for fusion weldment. These cut tubes are assembled to create various duct assemblies used on commercial aircraft, e.g., for distributing engine bleed air, thermal anti-ice heat air flow, air conditioning flow and the like.
Control of molten spatter, or molten metal, generated during the cut operations, is required to prevent damage to the duct or tube. The design of the LTC orbits the laser cutting head, in a planar motion, around the stationary tube or duct. As the material is melted, a molten plume of spatter is ejected towards the inside wall of the duct or tube. Without a method or apparatus to control and manage the spatter, it will impact and melt and resolidify and adhere to the internal tube or duct surface. The results would not be acceptable for production use, as this would require significant rework to remove the spatter.
A common method of controlling spatter during laser cutting operations is to coat the surfaces needing protection with an anti-spatter compound. This typically involves the use of low viscosity mineral oil. However, this defeats the purpose of the LTC system, which is to provide cuts xe2x80x9cready for weldxe2x80x9d with no requirement for manual solvent or tankline cleaning. All tube details are put through cleanline tanks prior to cutting following the tube or duct forming operations. The use of an anti-spatter compound would require post cleaning to meet fusion weld specification requirements. In addition, as these compounds are heated and vaporized, irritating and potentially hazardous fumes are created.
Methods and apparatus for preventing spatter have also been reported in prior publications, such as U.S. Pat. Nos. 4,532,403 and 5,994,667.
U.S. Pat. No. 4,532, 403 describes a method of coating the inside of a tube to be welded with a uniform layer of a surfactant that prevents laser burn through or laser weld spatter adhesion to the inside of the tube. Post-weld cleaning, as with the manual solvent method discussed above, is required and is undesirable.
U.S. Pat. No. 5,994,667 describes a mechanical method of preventing spatter adhesion in a cut tube by including a wire or mandrel of circular or angular cross-section that is positioned inside of the tube. The wire or mandrel can be moved during the cutting operation so that a new spatter accumulating surface is sequentially exposed to the laser. A fluid or gaseous coolant can also be used to cool and carry away the spatter or molten metal accumulated on the wire or mandrel. However, the device in this patent does not deflect the spatter for accumulation away from the cut tube and does not use a material such as disclosed in the present invention to chill the molten metal or spatter quickly so that it will fall out of the way where it can be accumulated and the apparatus of the invention can be reused.
Accordingly, it is an aspect of the invention to provide an anti-spatter tube for deflecting and accumulating molten metal or spatter that is created during a laser cutting operation being performed on the outer surface of a tube or duct which is placed in surrounding relation to the anti-spatter tube. The anti-spatter tube is made of copper and mounted on a mandrel inside the tube being cut, at the cut line, with its longitudinal axis perpendicular to the laser-cutting beam. An elliptical hole is cut in the side of the anti-spatter tube, and is rotated tracking the cutting laser head as it rotates around the duct or tube being cut during the cutting cycle to permit entry of spatter generated during the cutting cycle into the interior of the anti-spatter tube. A deflector plate mounted within the interior of the anti-spatter tube at an angle to the horizontal cutting plane directs the molten plume of metal or spatter down and away from the cutting plane and cutting operation. Copper is used as the anti-spatter tube material because it can withstand the heat of the molten plume, and its high thermal conductivity cools and solidifies droplets before they can stick to it. Any buildup of solidified material that does occur in the tube can easily be removed. The tube can be made to fit different diameter ducts being cut, and is self-aligning on the mandrel or post when mounted on the laser cutting center axis alignment post.
Another aspect of the invention is to provide a rotatable central post; a laser cutting nozzle orbiting the post adapted to cut a duct along a cutting plane generally perpendicular to the post which generates a plume of molten metal or spatter on the inner surface of the cut duct; a tube mounted on the central post concentric to the tube being cut for removing any spatter generated by cutting the duct; the tube having an opening which is elliptical in shape positioned in the cutting plane of the nozzle tracking and facing the nozzle as it orbits the duct and a deflector plate positioned at an angle to the cutting plane extending from a position adjacent to the top of the interior wall of the tube to the bottom of the interior wall for directing spatter to the bottom of the tube which has a bottom wall for collecting solidified spatter directed to it by the deflector plate.
Yet another aspect of the invention is the provision of an anti-spatter tube for use in a cutting process for preventing the build-up of spatter in the interior of a cut duct including an opening in the wall of the tube adapted to be positioned inside the duct in the cutting plane of a cutting nozzle, tracking and facing the nozzle as it orbits about the duct being cut; a deflector plate positioned at an angle to the cutting plane extending from the top of the interior wall of the tube to the bottom of the interior wall for directing spatter to the bottom wall of the tube where solidified spatter can be collected.
In a still further aspect of the invention, a method is provided for the removal of spatter or molten metal during a laser cutting operation by positioning an anti-spatter tube within a tube being cut, collecting spatter within the interior of the tube and deflecting the spatter to the bottom of the tube where it is cooled away from the cutting operation and solidified and easily removed without the use of potential chemical contaminants which have to be removed prior to and which would interfere with weldment of the cut tube.